Sometimes it's not bad where you start but you run into it along the way. Pretty sure it was spring of 2011 we got on the Missouri really early, like Mid-March. 2 buddies and I left the Hazelton ramp and headed S towards Ft Rice. Not far past the bend that runs you SW, we ran into fog so thick I couldn't see far enough to operate safely. I was in the channel running down the "Bismarck side". Neither GPS could pick up a signal. I came off plane and moved out of the channel and moved across until I bumped the sandbar on the "Mandan side", I didn't ever actually see it, just bumped it. The fog was so thick I couldn't see the shoreline at all, the GPS's couldn't get a signal, and for a good while, we really couldn't tell which way the boat was pointed. Obviously the boat had no choice but to float downstream but you could no longer intuit where that was. It was freaky.
Not a lot different that driving into a whiteout from a blizzard or ground-drifting. People can say:
"You shouldn't have been on the road in those conditions."
That might not have been the conditions 300Mi back where I started.